CHAPTER XI 

 THE BACTERIA (SCHIZOMYCETES) 



147. Introductory. In the preceding chapter it was stated 

 that the thallophytes constitute one of the four great divisions 

 of the plant kingdom. They are plants of xevy simple struc- 

 ture, and do not have roots, stems, and leaves. Some of them 

 are extremely simple, one-celled plants, and others are very 

 large and quite conspicuous. In methods of jDrodacing their 

 offspring thallophytes are also comparatively simple. Of all 

 the thallophytes the bacteria are simplest in structure, and we 

 shall consider them first in the series of plant groups. ^ 



^^'hat the bacteria are and how they live are questions of 

 Aery great hygienic as well as botanical importance. Bacteria 

 have sometimes been represented as wholly dangerous to men, 

 a conception very far from true. They have been called germs, 

 microbes, liaeilli, and microorganisms, often without any defi- 

 nite notions as to the real meaning of tliese names. Even the 

 fact that they are plants is not generally recognized by the 

 public, though for many years scientists have known it. What 

 the bacteria are. how they live, and how their life affects the 

 life of other living things are some of the questions to be 

 discussed in this chapter. 



148. Form. There is variation in the form of bacteria, as 

 there is among higher plants. Three groups, classed accord- 

 ing to form, are generally recognized, — the spherical (^coccus'), 

 rod (bacillus, Fig. 150), and spiral (sj^iriUum^ groups. There are 

 sphere forms of wide difference in sphericity, rod forms with 



1 Cultural experiments offer a better means of laboratory study of the 

 bacteria than does microscopic work. Demonstration microscopes will be 

 found helpful, however, in giving an idea of the size and form of a few of 

 the coiomon types of bacteria. 



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